U.S. patent number 6,571,795 [Application Number 09/775,424] was granted by the patent office on 2003-06-03 for breathing aid apparatus in particular for treating sleep apnoea.
This patent grant is currently assigned to Nellcor Puritan Bennett France Developpement. Invention is credited to Guy Bourdon.
United States Patent |
6,571,795 |
Bourdon |
June 3, 2003 |
Breathing aid apparatus in particular for treating sleep apnoea
Abstract
A compressor driven by a motor sends to a nasal mask a
breathable gas at a low positive relative pressure whereby the
motor is controlled to maintain the pressure in the delivery pipe
of the compressor substantially equal to a set point, independently
of the inspiration and expiration of the patient, a computer
receiving on an input a motor speed signal as a parameter
representative of the respiratory activity of the patient and
analyzing the motor speed variations whereby the computer will
increase the pressure set point if necessary or reduces the
pressure set point by a predetermined amount depending upon whether
there is a hypopnoea or the absence thereof.
Inventors: |
Bourdon; Guy (Verrieres le
Buisson, FR) |
Assignee: |
Nellcor Puritan Bennett France
Developpement (FR)
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Family
ID: |
9430721 |
Appl.
No.: |
09/775,424 |
Filed: |
February 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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839459 |
Apr 14, 1997 |
6283119 |
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360720 |
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Foreign Application Priority Data
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Jun 15, 1992 [FR] |
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92 07184 |
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Current U.S.
Class: |
128/204.23;
128/204.18; 128/204.21 |
Current CPC
Class: |
A61M
16/024 (20170801); A61M 16/0069 (20140204); A61M
2016/0027 (20130101); A61M 2016/0039 (20130101) |
Current International
Class: |
A61M
16/00 (20060101); A61M 016/00 () |
Field of
Search: |
;128/200.24,207.22,204.18,204.21,204.22,204.23 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 042 321 |
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Dec 1981 |
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EP |
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2 663 547 |
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Dec 1991 |
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FR |
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2 054 387 |
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Feb 1981 |
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GB |
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Other References
French Search Report for relating French Application No. 9211131,
dated Jun. 29, 1993. .
International Preliminary Examination Report for relating
International Application PCT/FR93/00902, dated Jun. 9, 1994. .
A first Opposition brief against the relating European Patent 0 662
009 B1, dated Feb. 15, 1999. .
Response to Opposition relating to European Patent 0 662 009 B1,
dated Oct. 8, 1999. .
A second Opposition brief against the relating European Patent 0
662 009 B1, dated Jan. 19, 2000. .
Response to second Notice of Opposition for European Patent 0 662
009 B1, dated Apr. 21, 2000. .
European Patent Office's decision on the Opposition for European
Patent 0 662 009, dated Sep. 27, 2001. .
Puritan-Bennett Brochure, Flow-By, Option 50, p. 1-6, dated Oct.
1986. .
Puritan-Bennett, 7200 Microprocessor Ventilator Service Manual,
Figure 2-1 Electro-Pneumatic System, dated Jun. 1983. .
Puritan-Bennett, 7200 Microprocessor Ventilator Operator's Manual,
dated Mar. 1986. .
The Future Begins . . . with Puritan-Bennett's 7200 Microprocessor
Ventilator, dated May 1983. .
Conference Proceedings, the New Generation of Mechanical
Ventilators, Respiratory Care, Jun. 1987, vol. 32 No. 6, p.
403-418. .
Grounds of Decision of Revocation relating to European Appln. No.
Ser. No. 95/930565.7--dated Oct. 16, 2001 (with translation). .
F. Clergue, M. Bakir & T. Tarakat, "Le respirateur Servo
Ventilator 900C," Departement d'anesthesie-reanimation (Pr P.
Viars) Groupe hospitalier Pitie, Salpetriere, Paris, p. 417-421,
dated 1984. .
Siemens News Letter, dated Nov. 1992. .
Siemens Technical Brochure of the SV300, dated Mar. 1992..
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Primary Examiner: Lo; Weilun
Assistant Examiner: Weiss, Jr.; Joseph F.
Attorney, Agent or Firm: Fulwider Patton Lee & Utecht,
LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No.
08/839,459 filed Apr. 14, 1997, now U.S. Pat. No. 6,283,119; which
is a continuation of U.S. application Ser. No. 08/360,720 filed
Dec. 12, 1994, now abandoned, which is a .sctn.371 application
claiming priority to PCT/FR93/00547 filed Jun. 9, 1993 and claims
priority to foreign application FRANCE 92 07184 filed Jun. 15,
1992.
Claims
What is claimed is:
1. An apparatus for controlling the positive pressure of breathable
gas to the airway of a patient, comprising: means for producing
breathable gas at positive pressure; means for controlling the
positive pressure of the breathable gas; means for determining an
amplitude of variation of the means for controlling the positive
pressure of the breathable gas; means for detecting the presence of
a hypopnoea as a function of the amplitude of variation; and means
for increasing the positive pressure of the breathable gas when the
means for detecting reveals the presence of a hypopnoea.
2. The apparatus of claim 1, further including means for decreasing
the positive pressure of the breathable gas when the means for
detecting reveals the absence of a hypopnoea.
3. The apparatus of claim 2, wherein the means for producing
breathable gas at positive pressure includes a drive motor operably
connected to a compressor, and wherein the means for controlling
the positive pressure includes a motor control operably connected
to the drive motor.
4. The apparatus of claim 3, wherein the means for controlling the
positive pressure further includes a pressure detector and a
comparator operably connected to the motor control.
5. The apparatus of claim 4, wherein the means for determining an
amplitude of variation utilizes a signal from the motor control
indicative of the rotational speed of the drive motor.
6. The apparatus of claim 1, wherein the means for detecting the
presence of a hypopnoea includes means for comparing a present
amplitude of variation with a threshold value calculated from at
least one previous amplitude of variation, wherein the means for
increasing the positive pressure increases the pressure of the
breathable gas when the present amplitude of variation is below the
threshold value.
7. The apparatus of claim 6, wherein means for detecting the
presence of a hypopnoea further includes means for calculating the
threshold value from an average of about eight previous amplitudes
of variation.
8. The apparatus of claim 1, wherein the means for detecting the
presence of a hypopnoea includes means for comparing the amplitude
of variation with a first threshold for a strong hypopnoea and a
second threshold for a weak hypopnoea, wherein the means for
increasing the positive pressure increases the pressure of the
breathable gas by a first incremental adjustment when the amplitude
of variation is greater than the first threshold for a strong
hypopnoea, and by a second incremental adjustment when the
amplitude of variation is between the first and second thresholds,
such that the first incremental adjustment is greater than the
second incremental adjustment.
9. An apparatus for the treatment of sleep apnoea, comprising: a
compressor configured to produce breathable gas at positive
pressure; a drive motor operably connected to the compressor; a
pressure detector in fluid communication with an outlet of the
compressor; a comparator having a first input, a second input and
an output, wherein the pressure detector generates a pressure
signal connected to the first input; a motor control operably
connected to the drive motor, the motor control configured to
generate a drive motor rotational speed signal, wherein the motor
control accepts the output of the comparator; and a computer
configured to accept the drive motor rotational speed signal, the
computer further configured to calculate an amplitude of variation
based on the drive motor rotational speed signal and to detect the
presence of a hypopnoea, wherein the computer is configured to
generate a pressure set point signal connected to the second input
to the comparator, such that the set point is calculated to
increase the positive pressure of the breathable gas when the
amplitude of variation is indicative of a hypopnoea.
10. The apparatus of claim 9, wherein the computer is further
configured to generate the pressure set point signal so as to
decrease the positive pressure of the breathable gas when the
amplitude of variation is indicative of the absence of a
hypopnoea.
11. The apparatus of claim 10, wherein the computer is further
configured to compare the amplitude of variation with a threshold
value, wherein the computer increases the pressure set point when
the amplitude of variation is lower than the threshold value.
12. The apparatus of claim 11, wherein the computer is further
configured to calculate the threshold value from an average of
about eight previous amplitudes of variation.
13. The apparatus of claim 12, wherein the computer is further
configured to increase the pressure set point when the amplitude of
variation remains below the threshold value for a predetermined
period of time.
14. The apparatus of claim 9, wherein the computer is further
configured to compare the amplitude of variation with a first
threshold for a strong hypopnoea and a second threshold for a weak
hypopnoea, wherein the computer increases the pressure set point by
a first incremental adjustment when the amplitude of variation is
greater than the first threshold for strong hypopnoea, and by a
second incremental adjustment when the amplitude is between the
first and second thresholds, such that the first incremental
adjustment is greater than the second incremental adjustment.
15. A method for controlling the positive pressure of breathable
gas to the airway of a patient, comprising: producing breathable
gas at positive pressure; providing a controller to adjust the
positive pressure of the breathable gas; determining an amplitude
of variation as a function of a signal from the controller; and
increasing the positive pressure of the breathable gas when the
amplitude of variation reveals a hypopnoea.
16. The method of claim 15, further including reducing the positive
pressure of the breathable gas when the amplitude of variation
reveals the absence of a hypopnoea.
17. The method of claim 16, further including comparing the
amplitude of variation with a threshold value, and increasing the
positive pressure of the breathable gas when the amplitude of
variation is lower than the threshold value.
18. The method of claim 17, further including calculating the
threshold value from an average of about eight previous amplitudes
of variation.
19. The method of claim 18, further including increasing the
pressure set point when the amplitude of variation remains below
the threshold value for a predetermined period of time.
20. The method of claim 15, further including comparing the
amplitude of variation with a first threshold for a strong
hypopnoea and a second threshold for a weak hypopnoea, and
increasing the positive pressure of the breathable gas by a first
incremental adjustment when the amplitude of variation is greater
than the first threshold for strong hypopnoea, and by a second
incremental adjustment when the amplitude of variation is between
the first and second thresholds, such that the first incremental
adjustment is greater than the second incremental adjustment.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a breathing aid apparatus, in
particular for treating people which are prone to the disease
called "sleep apnoea".
Sleep apnoea syndrome (SAS) is the accumulation of signs as well as
their consequences due to the periodic interruption of respiration
during sleep. The re-establishment of respiration generally only
occurs when the person concerned wakes up. This phenomenon can
occur several hundred times per night, with interruptions of 10
seconds or more each time.
Three types of apnoea syndrome exist, each corresponding to a
particular pathology.
The first type, which is the most common, is obstructive apnoea. It
results from an obstruction of the upper respiratory tracts caused
by a collapse of the tongue and the palate. The respiratory
movements continue, but because of this obstruction, air can
neither enter nor leave the lungs.
The second type, which is rarer, is called "central apnoea". It is
produced when the respiratory center of the brain no longer
controls respiration. In the absence of a signal originating from
the brain, the respiratory muscles do not function and air can
neither enter nor leave the lungs.
The third type is mixed apnoea which is a combination of the two
previous types, the start of the apnoea being of central type.
In the case of obstructive apnoea and mixed apnoea, treatment by
continuous positive pressure is the most commonly used. This
technique consists of permanently applying, via a nasal mask
connected by a pipe to a pressure generating apparatus, a low
positive relative pressure in the upper respiratory tracts in order
to avoid their obstruction. This pressure prevents the tongue and
palate from sticking together. The result is immediate: interrupted
respiration is re-established, the lungs receive the oxygen they
need and the person sleeps much better.
The optimum value of the pressure corresponds to the minimum
allowing the suppression of apnoeas and the oxygen desaturations
which result in the blood.
Determination of this optimum pressure is carried out in the
laboratory, by subjecting the patient to a polygraph recording, and
by progressively raising the level of pressure applied to the
patient until the disappearance of respiratory incidents.
The treatment described previously, which consists of applying a
constant pressure level to the patient throughout the night, has
certain deficiencies.
In fact, the frequency and extent of apnoeas vary during the night
according to the stage of sleep the patient is in. Also, they vary
over time as a function of the development of the condition of the
patient (gain or loss of weight, absorption of alcohol before going
to sleep . . . ).
Therefore, the treatment pressure determined by the prescription is
not necessarily adequate subsequently. Now, control recordings
cannot be carried out regularly, due to their cost and the
significant burden on sleep laboratories, connected with the large
number of patients to be treated.
In addition, the patient is subjected to an identical pressure all
night, whereas depending on the stages of his sleep, a lower
pressure may be sufficient, or a higher pressure may be necessary.
Now, the lower the average pressure applied during the night is,
the better the patient's comfort will be and therefore his
acceptance of the treatment, and the more the deleterious effects
linked with too high a pressure will be minimised.
SUMMARY OF THE INVENTION
The aim of the present invention is to propose a breathing aid
apparatus which allows the treatment to be optimized as a function
of the effective needs of the patient at each stage of
treatment.
According to the invention, the breathing aid apparatus, in
particular for treating sleep apnoea, comprising means of producing
a flow of breathable gas under a low positive relative pressure,
and means for leading this flow to a respiratory mask, is
characterized in that in addition the apparatus comprises means of
acquiring a parameter representative of the respiratory activity of
the patient, and automatic adjustment means for increasing the
pressure applied at least when the representative parameter is
indicative of a hypopnoea, and for reducing the applied pressure
when the representative parameter is indicative of normal
respiration over a predetermined time.
The term "hypopnoea" encompasses the phenomena of the total
disappearance of respiration, and can also include certain
phenomena of partial disappearance of respiration, due to a partial
obstruction of the upper respiratory tracts.
Thanks to the invention, the treatment apparatus is no longer a
simple constant pressure generator, but becomes an apparatus
capable of detecting hypopnoeas and of adjusting the pressure level
in order to suppress the hypopnoeas.
In this way, thanks to the apparatus, each time a hypopnoea is
detected, the pressure is increased, preferably by increments,
until the hypopnoea ceases. When no hypopnoea has occurred for a
defined period of time, the pressure is reduced by a predetermined
value.
This process allows hypopnoeas to be put to an end while
permanently minimizing the applied pressure.
Preferably, the pressure cannot go below a lower threshold defined
by the consultant and set on the apparatus, and of course it cannot
exceed the maximum value that the apparatus is capable of
delivering, or a maximum value defined by the doctor.
Other characteristics and advantages of the invention will become
apparent from the description below, with reference to the
non-limitative examples.
BRIEF DESCRIPTION OF THE DRAWINGS
In the attached drawings:
FIG. 1 is a diagram of an apparatus according to the invention;
FIG. 2 is a flow chart for the operation of the computer of FIG.
1;
FIGS. 3 and 4 are diagrams similar to FIG. 1 but relating to two
other embodiments; and
FIG. 5 is a flow chart of the operation of the computer of the
embodiment of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The apparatus represented in FIG. 1 comprises a compressor 1
capable of producing through its delivery pipe 2 a breathable gas
at a positive relative pressure, i.e. measured relative to
atmospheric pressure, which depends on the rotational speed of the
drive motor 3. In a non-represented manner, the compressor 1 is of
a type which produces the positive relative pressure by a turbine
for propelling breathable gas. The delivery pipe 2 is connected to
a nasal mask 4 by a flexible tube 6. The nasal mask 4 is intended
to be applied to the patient's face, for example by means of a
strap. The mask 4 includes an opening 7 allowing the patient to
expire despite the flow in the opposite direction coming from the
compressor 1.
A comparator 8 permanently compares the pressure P.sub.m detected
in the delivery pipe 2 of the compressor 1 by a pressure detector 9
with a pressure set point P.sub.c applied to the other input 11 of
the comparator 8. As a function of the result of the comparison,
the comparator 8 supplies at its output 12 a signal applied to a
motor control device 13 to reduce the rotational speed of the motor
3 when the pressure measured by the detector 9 is greater than the
pressure set point, and to increase the rotational speed of the
motor 3 and therefore the pressure at the delivery pipe 2 when the
pressure measured by the detector 9 is lower than the pressure set
point.
In this way, the pressure at the delivery pipe 2 and therefore in
the nasal mask 4, is approximately the same during the inspiration
phases and during the expiration phases of the patient.
During the inspiration phases, a relative low pressure tends to be
created at the delivery pipe 2 of the compressor 1, and maintaining
the pressure at the set point value requires an increase in the
rotational speed of the motor 3.
On the other hand, during the expiration phases of the patient, an
excess pressure tends to be created at the delivery pipe 2, and
maintaining the pressure at the set point value requires a decrease
in the rotational speed of the motor 3.
Consequently, when the respiration of the patient is normal, the
rotational speed of the motor 3 follows a periodical curve.
According to the embodiment in FIG. 1, a signal representative of
the rotational speed of the motor 3 is applied by the control
device 13 to the input 14 of a computer 16 whose function is to
analyze the curve of the speed of the motor 3 as a parameter
representative of the respiratory activity of the patient, and to
modify the pressure set point P.sub.c applied to the input 11 of
the comparator 8 as a function of the result of this analysis.
In a general fashion, when the analysis of the curve of the
rotational speed of the motor reveals a hypopnoea situation, the
computer 16 increases the pressure set point.
On the other hand, if the analysis of the curve of the speed of the
motor reveals an absence of hypopnoea for a certain predetermined
period of time, the computer reduces by a predetermined amount the
pressure set point.
The computer 16 is connected to a manual control 17 allowing the
minimum pressure set point P.sub.min authorized by the doctor for
each patient to be adjusted.
There will now be described with reference to FIG. 2, the flow
chart according to which, essentially, the computer 16 is
programmed.
In what follows, by "hypopnoea" is meant the symptom consisting
either of an abnormal lowering (for example by 50%) of the
respiratory activity, or the symptom of total apnoea consisting of
the complete disappearance of respiratory activity.
At the start, the pressure set point P.sub.c is chosen to be equal
to P.sub.min, i.e. the minimum pressure set point chosen using the
manual control 17 (stage 18).
In stage 19, the values An-8, An-7, . . . , An-1 of the amplitude
of the motor speed variation during the eight respiratory cycles
before the one which is currently being analyzed, are arbitrarily
set equal to a value A0 which is relatively low.
Then, in stage 21, the average of the amplitudes of the eight
previous cycles (average M) is calculated and two thresholds S1 and
S2 are calculated with for example:
In stage 22, the extreme values of the rotational speed of the
motor are sought.
In order to do this, the rotational speed of the motor at each
execution cycle of the program is stored in memory. A maximum or
minimum is only validated if the speed has then varied sufficiently
so as to be back from this maximum or minimum by a value at least
equal to threshold S2.
In other words, as the threshold S2 is greater than half of the
average of the previous amplitudes, a given extreme value will only
be processed if the speed again then reaches a value beyond that of
the average of the speeds. In particular, if respiration stops
(total apnoea), the speed of the motor assumes its average value
and the previous extreme value is not validated. More generally, if
an amplitude lower than threshold S2 tends to become established,
it will no longer be possible to validate the extreme values.
After a period of time T1 equal for example to 10 seconds, this is
detected in the following test 23. In the absence of an extreme
value for 10 seconds, one follows the path "detection of strong
hypopnoea" 24 of the flow chart, in which the four amplitudes An-8
. . . An-5 which are the oldest values still in memory are reduced
to the relatively low value of A0. The aim of this is to reduce the
thresholds S1 and S2 for the next calculation cycle so as to make
the resumption of respiratory activity easier to detect.
Returning to test 23, if an extreme value was found within the 10
previous seconds and if this extreme value is the same as that
already processed during the previous calculation cycle, one
returns to stage 23 in order to search for extreme values.
If, on the other hand, the extreme value is new, one passes via
stage 26 for calculating the new amplitude An, then, stage 27,
storing in memory the amplitude An while simultaneously deleting
the oldest amplitude in memory An-8.
In stage 28, the newly-calculated amplitude An is compared with the
largest S1 of the two thresholds.
If the newly-calculated amplitude An is greater than threshold S1,
one follows normal respiration path 29 which will be described
further on.
In the opposite case, i.e. if the amplitude is between thresholds
S1 and S2, it is considered that a weak hypopnoea 31 exists.
Whether strong hypopnoea 24 or weak hypopnoea 31 has been recorded,
a test 32 is carried out in order to determine whether there was
already a hypopnoea during the previous 30 seconds. If the result
is negative a number MAP is reset to zero. MAP corresponds to the
total increase in pressure in the previous 30 seconds.
If, on the other hand, there was hypopnoea during the previous 30
seconds, the MAP number is not reset to zero.
The following stage 33 consists of adding a relatively high
increment to the MAP number if strong hypopnoea was detected, and a
relatively low increment if weak hypopnoea was detected. Then, in
stage 34, a test is carried out to establish whether the MAP number
is greater than 6 cm of water (6 hP.sub.a). If the result is
negative, stage 36, an increment X, being high or low depending on
the strength of the hypopnoea, is added to the pressure set point
P.sub.c. If, on the other hand, MAP exceeds 6, the pressure set
point P.sub.c is only increased to the extent that the total
increase in the previous 30 seconds is equal to 6 (stage 37).
The aim of this is to avoid increasing the pressure excessively to
treat a single hypopnoea: if an increase of more than 6 cm of water
is necessary to treat a hypopnoea, it is because there is some
anomaly and it would be better to wake the patient up.
Then, the new pressure set point is applied to the comparator 8 in
FIG. 1 on the condition that it does not exceed the maximum
pressure set point P.sub.max. If the pressure P.sub.c exceeds
P.sub.max, the set point applied to the comparator 8 is equal to
P.sub.max (stage 38). One is then returned to stage 21 in which the
thresholds are calculated. If the strong or weak hypopnoea which
was detected during the previous cycle is still not alleviated, the
pressure set point will be increased by a new increment and so on
until the total pressure increase MAP within 30 seconds reaches 6
cm of water or until the hypopnoea is alleviated.
In this way, the amplitude is compared to two different thresholds,
one to detect strong hypopnoeas, including the total hypopnoeas,
and to apply a relatively swift increase in the pressure set point,
the other to detect weak hypopnoeas, resulting from a partial
obstruction of the upper respiratory tract, and to apply a clearly
milder increase in pressure.
One of the important features of the invention consists of
analyzing the parameter representative of respiratory activity (the
speed of the motor 3) not by comparison with absolute thresholds,
but by comparison with the respiratory activity which has just
preceded the respiratory anomaly. In fact, it has been noted that
respiratory activity varies greatly during sleep, to the extent
that an activity which would be considered normal during a certain
phase of sleep can correspond to a hypopnoea in another phase of
sleep.
Returning to path 29 of the flow chart, this leads to a test 39 for
determining whether a time T has passed without detecting a
hypopnoea. If the result is negative, one returns to stage 21 in
which the thresholds are calculated.
If, on the other hand, a time T2, for example equal to 30 minutes,
has passed without a hypopnoea, the pressure set point is reduced
by, for example, 2 cm of water. In this way one provides an
opportunity to bring the pressure applied to the patient to a lower
value if this is possible.
However, if the new pressure set point thus became lower than the
minimum pressure as set with the manual control 17 of FIG. 1, the
pressure set point is simply reset equal to the minimum pressure
set. Then, once again, one is returned to stage 21 in which the
thresholds are calculated.
In the example represented in FIG. 3, which will only be described
with regard to its differences relative to that of FIG. 1, a flow
rate detector 41 is placed on the delivery pipe 2 of the compressor
1 whose signal is sent to an input 42 of the computer. On the other
hand the computer no longer receives a signal corresponding to the
rotational speed of the motor. It is now the flow rate signal
provided by the detector 41 which provides the computer with the
parameter representative of the respiratory activity. When the
patient inspires, the flow rate detector 41 reveals a higher flow
rate than when the patient expires. In other words, the variations
in flow rate work in the opposite sense to those of the speed of
the motor 3. Apart from that, nothing is changed, and the flow
chart of FIG. 2 is valid for the embodiment of FIG. 3, with the
exception that in stage 22 in which the extreme values are sought,
the word "speed" must be replaced by the words "flow rate".
The example of FIG. 4 corresponds to a simplified version.
In this example, which will only be described with regard to its
differences relative to that of FIG. 1, there is no pressure
regulation at the delivery pipe 2, i.e., apart from situations of
apnoea or hypopnoea, the motor 3 rotates at the same speed whether
the patient inspires or expires. The pressure at the delivery pipe
2 is therefore relatively low when the patient inspires and
relatively high when he expires. Therefore, the pressure at the
delivery pipe 2 constitutes a parameter representative of the
respiratory activity and it is, as such, detected by the pressure
sensor 9. The computer 16, which receives the pressure signal 9 on
an input 43, analyzes the pressure curve and provides the control
device 13 of the motor 3 with a signal for increasing the speed of
the motor 3 when the variations in pressure indicate a situation of
hypopnoea, and for decreasing the speed of the motor 3 when any
situation of hypopnoea has not been alleviated within a
predetermined period of time, for example 30 minutes.
FIG. 5 represents a schematic flow chart according to which the
computer 17 of FIG. 4 can be programmed.
At the start, the speed V of the motor is adjusted to a value
V.sub.min (stage 44) set with a manual control 46 (FIG. 4).
Then one passes to stage 47 in which hypopnoeas are detected
according to the amplitude of the variations in pressure. This
stage can correspond to stages 21 and 22 of FIG. 2, except that it
is then applied to the pressure instead of being applied to the
speed of the motor. In the absence of hypopnoea, one passes via
path 48 in which the speed of the motor is reduced by a
predetermined value n' if a time T2, for example 30 minutes, has
passed without hypopnoea, without however lowering the speed to a
value which is less than the set speed V.sub.min.
In the case of a hypopnoea being detected during a period of time
greater than or equal to a value T.sub.1 of for example 10 seconds,
the speed V is incremented by a predetermined value n, without
however allowing the speed to exceed a value V.sub.max.
Consequently, in this simplified example, only a single degree of
intensity of hypopnoea is distinguished and when the hypopnoea is
detected, one and the same mode of action is envisaged in every
case, i.e. an incrementation of the speed of the motor according to
one predetermined step and one only.
Of course, the invention is not limited to the examples as
described and represented.
In the computers of the embodiments according to FIGS. 1 and 3 a
program could be envisaged which distinguishes only one type of
hypopnoea, or on the other hand, the embodiment according to FIG. 4
could be equipped with a program which processes in a different way
the weak hypopnoeas and the strong hypopnoeas as was described with
reference to FIG. 2.
While particular forms of the invention have been illustrated and
described, it will also be apparent to those skilled in the art
that various modifications can be made without departing from the
spirit and scope of the invention. Accordingly, it is not intended
that the invention be limited, except as by the appended
claims.
* * * * *